This invention relates to a deflecting method for scanning and a deflector for deflecting a charged particle beam such as an ion beam with scanning. This invention particularly relates to a deflecting method and a deflector suitable for deflecting a charged particle beam with a relatively large current or a charged particle beam with a relatively large diameter. The charged particle beam with the relatively large diameter represents, for example, a charged particle beam having a flattened cross-sectional shape in which its horizontal width is greater than its vertical width. Note that “horizontal” which will hereinafter be referred to represents one axis in a plane in a direction perpendicular to a center axis of a beam trajectory and does not necessarily represent a horizontal axis. Likewise, “vertical” represents one axis in the plane in the direction perpendicular to the center axis of the beam trajectory and does not necessarily represent a perpendicular or vertical axis, and specifically represents the axis that is perpendicular to the foregoing axis of the horizontal direction in the plane in the direction perpendicular to the center axis of the beam trajectory. This invention is suitable for application to an ion implantation method and an ion implantation system but is not limited thereto.
Description will be briefly given about a structure of the ion implantation system. In this specification, an ion beam falls under the category of a charged particle beam and the charged particle beam may hereinafter be referred to simply as a “beam”.
As is well known, in the ion implantation system, a beam is extracted from an ion source through an extraction electrode. The extracted beam is analyzed by a mass analysis electromagnet device and a mass analysis slit. As a result of the mass analysis, only a necessary ion species is selected. The selected ion is implanted into a substrate such as a silicon wafer.
Normally, the ion implantation system is provided with a deflector for deflecting the beam in order to scan the surface of the substrate with the beam. Deflectors of this type include a magnetic deflector and an electrostatic (electrical field) deflector. Description will be briefly given about structures, merits and demerits of the magnetic deflector and the electrostatic deflector.
The magnetic deflector comprises an electromagnet composed of at least two magnetic pole pieces confronting each other through a gap defined therebetween and a coil. A current supplied to the coil generates in the gap a magnetic field that deflects the beam. By changing the current supplied to the coil, the beam passing through the gap is magnetically deflected. The magnetic deflector has a merit of facilitating uniform generation and distribution of a magnetic field over a wide region as compared with the electrostatic deflector. However, the magnetic deflector has a demerit that a structure thereof tends to be large and complicated and further the power consumption thereof is large. In addition, the magnetic deflector also has a demerit that the magnetic field tends to leak and, as a scanning frequency increases, it becomes more difficult to generate the magnetic field. Moreover, in the magnetic deflector, there is an instant when a deflection angle of the beam becomes zero (i.e. the beam goes straight on) and, in this instant, the magnetic field disappears. While the magnetic field disappears, secondary electrons neutralizing the beam are dispersed so that a diameter of the beam increases. As a result, the beam diameter differs between when the deflection angle is zero and when the deflection angle is other than zero.
On the other hand, the electrostatic deflector comprises at least two opposite electrodes confronting each other through a gap defined therebetween. A scanning voltage is applied across the two opposite electrodes. The scanning voltage generates in the gap an electrical field that deflects a beam passing through the gap. By changing the scanning voltage, the beam passing through the gap is electrostatically deflected (e.g. see JP-A-2003-513419). The electrostatic deflector has a merit that it can be more compact in structure and requires less power consumption as compared with the magnetic deflector. However, the electrostatic deflector has a demerit that a uniform electrical field is difficult to generate and the beam after deflection is inferior in quality as compared with that in the magnetic deflector.
Incidentally, in the deflection of the beam, when a beam current is large or the beam has a flattened cross-sectional shape, i.e. a cross-sectional shape that is horizontally elongated, it is difficult for the conventional electrostatic deflector to cope with it and, therefore, improvement in performance of the deflector is essential.
Specifically, when a beam having a horizontally elongated cross-sectional shape is deflected in its major-axis direction (horizontal-width direction), it is required that the beam be deflected at substantially the same deflection angle at any portions of the cross-section of the beam. Note that even if variation in deflection angle occurs in the deflection of the beam, it is assumed that no problem is raised when the variation is sufficiently small or can be easily corrected.